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[EnergyPlus_Support] Doubts on Low Temperature Radiant System Hydronic
Hi all,
I? m sorry for repeating the sending of this mail but until now I didn?t
find an explanation for the simulation results and I hope that somebody
could help me.
Thanks in advance for your help.
Problem Description:
I?m studding the possibility of implementation of a radiant floor system in
a building to determine the impact on occupant thermal comfort and
ventilation energy savings.
To do this I?ve created a simple monozone rectangular building model with an
area of 5 000 m2 and high internal gains.
In what concerns to HVAC systems two models were created:
1. With compact HVAC I?ve created a VAV system to provide fresh air
and to control zone temperature.
2. The second model was created by adding to the first model a Low
Temp Radiant System:Hydronic system. The radiant system has heating and
cooling priority 1 and the VAV system has heating and cooling priority 2.
Because water supply temperature is different in the two systems, two plant
loops were simulated.
The input defined to the low temp radiant system is as follows:
!- =========== ALL OBJECTS IN CLASS: LOW TEMP RADIANT SYSTEM:HYDRONIC
===========
LOW TEMP RADIANT SYSTEM:HYDRONIC,
Resistive DVB_mall Radiant Floor, !- name of hydronic low temperature
radiant system
On-8h-24h, !- availability schedule
DVB_mall, !- Zone name
S_DVB_mall_0_0, !- Surface name or group
0.02, !- Hydronic tubing inside diameter {m}
autosize, !- Hydronic tubing length {m}
MRT, !- temperature control type
autosize, !- maximum hot water flow {m3/s}
Resistive DVB_mall Radiant Water Inlet Node, !- heating water inlet
node
Resistive DVB_mall Radiant Water Outlet Node, !- heating water outlet
node
4, !- heating control throttling range {deltaC}
Radiant Heating Setpoints, !- heating control temperature schedule
autosize, !- maximum cold water flow {m3/s}
DVB_mall Cooling Water Inlet Node, !- cooling water inlet node
DVB_mall Cooling Water Outlet Node, !- cooling water outlet node
4, !- cooling control throttling range {deltaC}
Radiant Cooling Setpoints; !- cooling control temperature schedule à
25 ºC
I?m using 1 dimension for CTF calculation
Taking a look to simulation results everything seems to be working as
expected. Zone air temperature is controlled, both systems are operating and
is noticeable the air flowrate reduction in the air handling system when
radiant floor is present.
The autosized parameters to the radiant floor were:
Component Sizing, LOW TEMP RADIANT SYSTEM:HYDRONIC,
RESISTIVE DVB_MALL RADIANT FLOOR, Maximum hot water flow [m3/s],
0.91287E-03
Component Sizing, LOW TEMP RADIANT SYSTEM:HYDRONIC, RESISTIVE DVB_MALL
RADIANT FLOOR, Maximum cold water flow [m3/s], 0.17932E-01
Component Sizing, LOW TEMP RADIANT SYSTEM:HYDRONIC, RESISTIVE
DVB_MALL RADIANT FLOOR, Hydronic tubing length [m], 32736.
To analyze the effect of autosized parameters, in particular the Hydronic
tubing length, simulations with model 2 were carried by reducing the tubing
length to 16 000 and 8 000 m . The maximum hot and chilled water flow rate
fields were filled with the calculated values presents above. Tubing
diameter value was maintained.
By reducing the tubing length (less heat transfer area) I was expecting that
my radiant floor system could remove less load but simulation results were
exactly the same for the two additional tubing lengths studied when compared
with the original case.
I took a look at the Engineering Reference Manual and for what I understood
and by the equations presented, the simulation should be affected by heat
transfer area.
Could you help me on this topic? Am I missing something?
Thanks in advance for your help
Best Regards
Filipe Madureira
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